Method for preparation of rhenium



United States 2,935,399 METHOD FOR PREPARATION or 1 j Ivor 'Eugene Campbell, Gahanna, and 'Danny Mees -Rosenbaum, Columbus, Ohio, assiguors, by/mesne'as. signments, to The Battelle Development Corporation, Columbus, Ohio, a corporation of Delaware 1 No Drawing. Application November 14, 1955 Serial No. 546,781

, Claims. c1.'75-s4 as molybdenite and gadolinite, and with somewhatric'her' sources being found in some molybdenite ore concentrates and in'flue-dust collections from copper ores containing molybdenite.

lice.

cordingly, is less than that of a metal body having a lesser amount of voids or porous sections. 7

An object of this invention is to provide a method for the preparation of rhenium metal of higher purity than has previously been available from crude rhenium metal containing potassium;

Another object of this invention is a method of pr'epa ration of substantially pure rhenium metal, wherein the rhenium metal is substantially free from impurities and wherein the potassium content is low enough to permit consolidation and fabrication.

Still another object of this invention is an improved process for recovery of a pure rhenium metal wherein impurities including potassium are eliminated or reduced to a negligible amount by forming a volatile rhenium halide, selectively volatilizing the rhenium halide, subsequently hydrolyzing the rhenium halide, and converting the hydrolysis productto the pure rhenium metal. 7

Further objects and advantages of this invention will be readily seen and appreciated as the same become better known and understood'by reference to the following detailed description when considered in conjunctionwith the specific'examples.

Thezinvention is a new and novel method of preparaliOIISOf substantially pure rhenium metal comprising the} combination of halogenation of a crude rhenium metal to a rhenium halide; selective volatilization of he rhenium halide; and conversion of the selectively volatilizedrhenium halide to a substantially pure rhenium metal, by means such as hydrolysis of the rhenium halide and reduction of the hydrolysis product to a substantially pure Numerous methods have been p'ublishedand patented for therecovery of rhenium salts or metals from ,the nat ural ores and concentrates relatively rich in rhenium, and are well known to those skilled in the 'art. For example, US. Patent 2,414,965 teaches a process for rheiiiuinrecovery from flue dust and US. Patent 1,911,943 teaches rhenium recovery from ores containing rhenium; Usually the last step in a rhenium-recovery process involves conversion of some rhenium compound into metallic;

rhenium as a powder, or as some consolidated form. This powdered or consolidated form of metallic rhenium thenneeds to'be further consolidated or compacted, as I by 'sint ering or melting, to obtain a sound, metallic struc- In the known rhenium separation or purification meta-1 ods where potassium perrhenate is an intermediate prod-" not or a starting compound, there is usually ;a reduction 'step to the crude rhenium metal and this crude rhenium metal frequently has been subjected to further process ture', suitable for metallurgical purposes.

steps for removal of impurities. However, the potassium oxide, which is formed as a by-product in the potassium perrhenate, reduction, is extremely diflicult if not impossible to remove completely from the crude rhenium metal by leaching, washing, dialysis, or by other presentday wet chemical methods.

rhenium metal that for practical purposes is freeof potassium. The powder size of the pure rhenium metal is such as to lead to easy densification by methods standard to w the powder metallurgy art. g In the practice of this invention, potassiumperrhenate,

as sold commercially, is a suitable starting material. Al-

ternatively, potassium perrhenate, an important saltof perrhenic acid, may be prepared as a result 'of neutrali- While rhenium is a relatively costly metal, it isfindin g increasing use as a special-purpose material. Many potential high-temperature applications for rhenium exist,

since, among the metals, only tungsten has a higher melting point. 1 I

Rhenium metal containing impurities is difi'icult to f abricate. For example, potassium in excessive amounts in the rhenium apparently inhibits densification. For rhenium, it appears that a minimum sintered density or approximately 70 percent of the theoretical density of the solid :metal of 21.0 grams per cubic centimeter is needed for successful cold-working of the rhenium metal.

-- .Densification is to be understood as being a measureof the relative compactness of the metal body as'compared tojthetheoretical density of the solid metal. The dens1' fication of a metal body with voids or porous sections, ac-

uct to a negligible amount.

zation of perrhenic acid with potassium hydroxide or, as a result of the reaction of potassium chloride with perrhenic acid. Perrhenic acid may be prepared in several ways. One ofthe most common is the combination or solution of rhenium heptoxide with water. Numerous other methods for the preparation of potassium perrhenate are known to those skilled in the art.

Alternatively, ammonium perrhenate may be used as the starting material. be prepared by the neutralization of perrhenic acid with ammonium hydroxide; or the ammonium perrhenate may be prepared from potassium perrhenate by a reduction to the rhenium metal with subsequent oxidation of the rhenium metal to arhenium oxide which is treated with ammonium hydroxide; or ammonium perrhenate may be prepared by other means well known to those skilled 'in the art. v

Alternatively, scrap rhenium metal or crude rhenium metal which, as such, is not capable of fabrication may be used as the starting material or maybe used in combination with crude rhenium metal obtained from numerous starting materials.

Any, or all, or combinations of any or all, of the rhenium materials mentioned may be used as suitable alternative starting materials where it is desired to reduce potassium and other impurities in the rhenium metal prod- Inthe practice of this invention wherein potassium perrhenate is the starting material, the first step of the process is the reduction of the potassium perrhenate to a crude rhenium metal.

-' Patented Mayi3,"l'960 The ammonium perrhenate may The second process step is the, halogenation of the crude rhenium metal to a volatile rhenium halide. The third process step is the SBICCUV? masses volatilization'ofthen'henium halide. The fourth process step. isthe. subsequent hydrolysisof the.volatile.rhenium halide, and the fifth processstep is the reduction of the products of hydrolysis to rhenium metal containing only a, negligible amount of;potas.sium' and. other impurities;

In the practice of this:invention-wherein.ammonium perrhenate is; the. startingmaterial, the. first step isv the heating:- of; ammonium perrhena-te in a. hydrogen. atmos phere to, obtaina. crude rhenium metal; The secondstep and subsequent remaining steps of the. process are-the same as-;in the practice of; the invention wherein potassium perrhenate is the starting material.

In the practice of this inventionwherein scraprhenium metal or crude'rhenium. metal. having a'potassium. content, which, as such, is not capable. of: fabrication; or wherein crude rhenium metal in. combination. with scrap metal, or with metal incapable of fabrication, are. theillustrative. and not as limiting. flIQE QPEEOfZ the-present invention.

Example I Rheniurn powder was prepared by the hydrogen reduction of commercial potassium perrhenate in the following manner: approximately 1000 grams of'potassium perrhenate were reduced in a heated stainless steel vessel by the addition of hydrogen gas. Prior to. the addition of hydrogen gas, the vessel and contents were preheated to 250 C. and this temperature was maintained for the.

first hour of reduction. At this timethe vessel andcontents were heated to 500 C. and maintained'at-SOOF C. for approximately three hours. Thered'uction may be considered completed when condensation of'moisture can no longer be detected from the exiting gas. Then, the vessel andcontents were permitted to cool to approximately room temperature and the hydrogen gas flow stopped. The contents were removed from the.vessel. The product-was leached with distilled water to remove substantial amounts of potassium hydroxide. The prod;

uct was'then returned to thereduction vessel and reduced further by hydrogen gas with the vessel and contents at 1000 C. for two additional hours to obtain the crude, rhenium metal powder. The crude rhenium metal was leached with distilled water, then leached with a. dilute aqueous acid solution of percent hydrochloric acid by volume, and then leached withadditional distilled water in an effort-to remove potassium from the crude rhenium metal.

Approximately 93 percentof the rhenium was. recovered as crude rhenium metal powder. A chemical analysis was made of the crude rhenium metal powder obtained with the potassium content analyzing .50 percent.

Example I] The ammonium perrhenatefor this example a was prepared from potassium perrhenateby a-hydrogen reduction tothe rhenium metal with subsequent oxidation of the rhenium metal to a rhenium oxide which was treated with ammonium hydroxide to obtain theammonium perrhenate. Approximately 350' gramsof rhenium powder were prepared from ammonium perrhenateinthe fol lowingmanner: 500 grams of'finely divided ammonium perrhenate, having a potassium content of .47 percent, were heated gradually to 1000 C; in a closed Vycor vessel with pure, dry hydrogen gas passing for-approxi mately two hours'through an entrancetube intothevem The sel, circulating through the ammonium perrhenate, and exiting through an exit tubeattached to the vessel. Vycor is the name of a low-expansion glass consisting essentially of silica that is marketed and sold by the Corning Glass Company, Corning, New York. The ammonium perrhenate decomposed to give ammonium hydroxide, water, and a blackpowder. As the heating continued, the black powder was reduced by thehydrogen atmosphere to a crude rhenium metal powder. The heat was: discontinued and the hydrogen gas: flow.- continued; untiltheves'sel and product, rhenium metal, reached room temperature;

A chemical analysis was made of the crude rhenium metal powder obtained, with. the potassium content' analyzing .40 percent.

Example III The crude rehenium metal for this example was a composite mixture of crude rhenium metals prepared by the processes as illustrated in Examples I andII. Approximately 300 gramsof cruderhenium metal powder, having a. potassium content of. .40, percent, were, exposed. to. hydrogen gasat 800 C. for two hours by, passingthe hydrogen gas through the rhenium metal powder in. a. Vycor apparatus to convert any rhenium metal oxides present tocrude rhenium metal. The rhenium metal powder was; cooled to 700 C witha purgingflpw of helium gas-flowing through the apparatus.

The. helium. gas inlet was closed and, commercially. available tank chlorine gas admitted at. a.- ratesuflicientto maintain a. small positive pressure within the apparatus as shownby the flow from the exit line of the apparatus. The rhenium, metal powder wasconverted to rhenium pentachloride, which condensed in or near the exit flow line. The rhenium metal chlorinated at. a rate of approximately grams per hour with all the rhenium apparently converted to the pentachloride. The condensed rhenium pentachloride was flamed with a hand torch at intervals driving the pentachloride into a collecting vessel which. was maintained. at. approximately room. temperature.

The rhenium-,pentachloride was hydrolyzed by adding it slowly and cautiously to distilled water cooledto about 10 C. by an. ice bath. The reaction was accompanied. byvigorous boiling and the formation of an extremely fine particle-size precipitate. (If the hydrolysis is not, carried. out in cool waterthe yield is somewhat lower.) Theprecipitate wasfiltered from the filtrate onto medium retention filter paper. The precipitate Wasair-dried, and. then dried; further in a desiccator: using calciumsulfate hemihydrate-as a desiccant.

A- few grams of the dried precipitate. were reduced by hydrogen gasat 600- C. in one hour to obtain the purified rheniummetal. Later some additional. precipitate was reduced at 600 C. to obtain approximately 200 grams additional pure rheniummetal.

A chemical analysis was made on the purified rhenium. metal and the-total impurities found analyzed .05 per-- cent. Theanalysis showed; a 0.00 percent potassium content. The analysis for potassium hada sensitivity sufficient to detect potassium contents as. low as .001 percent.

Example IV Anapproximately BOO-gram mixture of approximately 50 percent crude rhenium metal and 50 percent scrap the process illustrated in Examples l and II, where in all previous runscrude rhenium metal containing in excessof .20 percent impurities was obtained. The exact impurity content of the scrap rhenium metal was not known. However, the scraprheniummetal was metal incapable; of fabrication because of insutficient densitication, and its"be'havior= under fabrication attempts resembled thatof rhenium metal containing suflicient potassium. to inhibit densification.

- The rhenium metal mixture was placed in a vesselof Vycor andthevessel and contents heated to 750 C.

' with a purge of helium flowing through the mixture and vessel, The helium fiowwas stopped and at the same instant a flow of commercially available tank chlorine gas was supplied to the. vessel and'con'tents. The chlorine gas flow was.continued for two hours i 15 minutes with the vessel and contents at 750 C. The rhenium metal chlorinated at a rate'of approximately 150 grams per hour. The volatile rhenium pentachloride was collected .The dried precipitate was reduced by hydrogen gas at 1 600 C. to-obtainpure rhenium metal with approximately 87 percent of the theoretical yield of obtained.

,Example I illustrates a conventional preparatlon of.

pure rhenium being crude rhenium metal from potassium perrhenate. I The crude'rhenium metal after several leachings, including onewith a dilute aqueous acid solution, still contained a substantialpotassium content.

Example II illustrates that a conventional method-of preparation of crude rhenium metal from ammonium perrhenate with a substantial potassium content gives a rhenium metal having a substantial potassium content.

Examples III and IV illustrate the method of this invention wherein crude rhenium, metals with a substantial potassium or impurity content are converted into pure rhenium metal. The potassium or total impurities in the product metal are negligible for metallurgical purposes. In'the' step of preparing the crude rhenium metal from potassium perrhenate by hydrogen reduction a maximum temperature of 500 C. is preferred. At a temperature of approximately 550 C., melting of the potassium perrhenateis likely to occur. While the hydrogen reduction of potassium perrhenate has been accomplished successfully at temperatures slightly above 500 C., dif- Ificulty has beenencountered when attempting to use a 550 C. temperature.

In the'step of halogenation of the crude rhenium metal, where the halogenation is a chlorination, temperatures ranging from 600 C. to 800 C. have been used. "A

7 temperature of 750 C. is the preferred chlorination temperature. The rate of chlorination appears to be dependent on the chlorination temperature with little increase in rate of chlorination at temperatures greater than 750 C., and with rapid decreases in the rate of chlorination at temperatures lower than approximately 600 C. In the separation of the precipitated product of the hydrolysis step, filtration time may be reduced substantially by bubbling carbon dioxide gas through the water containing the product for about 30 minutes before filtering. Rhenium remaining in the filtrate may be recovered by treating the filtrate with a small amount of 30 percent hydrogen peroxide solution to' obtain a perrhenic acid solution which may be neutralized by ammonium-hydroxide to obtain ammonium perrhenate which may be converted to crude rhenium metal for subsequent recycling in the process of this invention.

In the'step of hydrogen reduction of the product obtained from the hydrolysis of the volatilized rhenium halide, it is preferred that the temperature be raised stepwise to a maximum temperature of approximately 600 C. and that the maximum reduction temperature be maintained for a sufficient period of time to accomplish thereduction. Successful reductions of the hydrolysis product have been made at maximum temperatures as 6 high as 1'0oo c. The particle sizeof the rheniummetal obtained from the hydrogen reduction ofthe hydrolysis productappears to be. dependent on the reduction temperature with the finer particle size *obtained at the lower temperatures.

Numerous unsuccessful attempts were made tov metallurgically process crude rhenium metal as obtained from the hydrogen reductionof potassium perrhenate, as.illustrated in Example I, and from the decomposition-reduc tion of ammonium perrhenate, as illustrated in Example In a few instances proper pressing of the'crude rhenium powder was achieved, but in no instance, aftersintering, was a densification of the powder body; ob-- tained sufficient to permit metallurgical processing and fabrication, where the. potassium content of theserheniuin metals exceeded .05 percent. The crude rhenium metals in;

these unsuccessful metallurgical processing attempts generally had potassium contents ranging from 0.06 percent Varied particle-size crude rhenium to 0.60 percent. powders were utilized with insuflicient improvement in densification to permit metallurgical processing.

However, rhenium metals prepared by the method of this invention, as illustrated in Examples III and IV, with only a very small or negligible potassium content, were and" metallurgically processed. Almost invariably, densifications from sinter- 1 ing in excess-of 70 percent of theoretical density were obtained and'the sintered rhenium powder body was sucsuccessfully pressed, sintered,

cessfully metallurgically processed.

The preparation of a sintered metal rhenium body by pressing and sintering was in accordance'with known methods of the powder metallurgical art. The sintered and densified'rhenium metal body was metallurgically processed by suitably selected cold working of the body prior to heavier cold reductions. In the heavier cold reductions, annealing of the metal body was necessary and the amount of reduction was controlled and limited in a stepwise procedure in that a reduction of' the rheni um metal body was made, then the body wa'sia'nnealed. This was then followed by subsequent reductions plus.

annealings to eventually obtain the desired dimensions.

Pure rhenium metal prepared by the process of this invention, as illustrated in Example III and IV'was suc-; cessfully metallurgically processed and physical properties of the pure rhenium metal measured. Pure rhenium metal prepared, .as illustrated in Example III,'was pressed and sintered to obtain-la densification of approximately apercent of theoretical density. 'Annealed rhenium rods (0:051 in'ch in. diameter) from the. metallurgically processedrheniummetal, prepared as illustratedinExample III, gave a tensile strength of 171,000 p.s.i., an elongation of 15 percent, and, in the annealed state, a

Vickers hardness ofless than 300 V.H.N.

The physical properties of the pure rhenium metal,

prepared by the process of this invention, after metallurgi cal processing are at least the equivalent and generally are: superior to the physical properties of rhenium obtained by.-v

any other known process. For example, Agte and his coworkers in Physical and Chemical Properties of Rhenium,-Z. anorg. m. allgempChemg 119, 129-159' (1931), report atensile strength for rhenium of 70,000 p.s.i. for rhenium specimens preparedby a hot-wire deposition process.

rhenium metal with improved physical properties may be obtained. While the exact reason for the improved physical properties of the rhenium of this invention is unknown, it is believed and theorized that the minimization of potassium and other impurities in the rhenium has invention is not so limited and, that, as will be obvious Smum consisting of; fluorine. chlorine, and: bromine of: group VII, o f;the :periodic table maybe used in the haio gena iQn stem These members: of group VII of the periodic table are commonly known ashalogens and the generic rcactionofiamember: of the group with rhenium to;give;a;,rheniumhalide is, known ashalogenation.

It is. to. be: understood that rhenium halide as used inv the: specification; and; claims is, inclusive of all volatile halidesor volatile complex halidesof rhenium and fluorine, chlorine, and/orbromine'. his to be understood that'the'termrhenium chlorideas used'in the specification andthe: claims is'intended. to'include all volatile rhenium chlorides; Rhenium-chlorine binary compounds correspondingto: several oxidation statesareknown. In a like manner, rhenium fluoride includes; all volatile rhenium fluoridesv and; volatile: complex: fluorides. and rhenium bromide includesall volatile rhenium bromides ,or volatile: complex-bromides.

While the specific procedures. and examples givenv have. illustrated the conversion. of'the. selectively volatilized rheniumhalide to a substantially purerhenium metal by the. preferred,methodofihydrolysis of'the selectively V013: tilizled rheniumhalide and'reduction of the hydrolysis. product'toa substantially pure-rhenium metal, it is-tobe understood that. this: invention; is not so limited. Other means known to: thoseskilled; in the art may be used;

For; example; theselectively" volatilizedrhenium halide.

may be converted to a substantially pure-rhenium metal by hydrogenreduction, or by conversion to anoxide followed; bysubsequent reduction, or by other means well known to those skilled' in the art.

Thisinvention'permitsthe preparation of a pure rhenium metal ofadequate purity for metallurgical pm poses. The potassium and other impurities in the purifiedgrhenium metal are held' to a negligible'quantity, thus facilitating the consolidation of'the purified metallic rheniumztoa sound,- metallic istructureior metallurgical purposes: and: permitting the obtaining of improved physical properties in the sound, metallic structure.

While a: preferred method has been shown and described, it:will.beobvious to those skilled in the art that various changes and modifications may be made withoutydeparting from-the invention in its broadest aspectsand the appended claimsare intended to cover all such; changes and modifications as. follow within the true spirit and scope-of the-invention.

What is claimed is:

1. A method forobtaining asubstantially free-frompotassium, purified rhenium metal powder for metallurgicaLconsolidation and fabrication from a crude rhenium metal containing potassium, themethod comprising: preparing a volatilizatiou product by exposing the crude=rhenium metal containing potassium to a halogen selected from the group consistingoffi'uorine, chlorine, and'bromine at an elevated:temperature-sufficient to'form' and tovolatilize a'rhenium halide transferring the volatilization product in a gaseous state toa situs other'than the situs ofv the preparation of the-volatilization product; condensing the transferredvolatilization product; contacting the condensed 'volatilization product with water to form a'rhenium-hyd'rolysis product; and reducing the rhenium hydrolysis product with hydrogen to provide the substantially free-from-potassium, purified rhenium metal" powder.-

2'. Theamethod of: claim in" which: the halogen-is"- 3. The method of claim 1: inwhich thehalogen is.

chlorine.

4. The method of claim 1 in which the-halogen is bromine.

5'. Themethod of claim 1' in which the halogen is chlorine and in which the method includes thepreparation of the crude rhenium metal containing: potassium lay-a hydrogen reduction of potassium perrhenate.

6. The method of claim 1 in which the halogen ischlorine and in which the method includes the preparation of the crude rhenium metal containing potassium by a hydrogen reduction of ammonium perrhenate conmining potassium.

7. A. method for obtaining a substantially free-frompotassium, purified rhenium metal powder for metallurgical consolidation and fabrication from acrude rhenium metal containing potassium, the method comprising: exposing the crude rhenium metal containing potassium to=a= halogen selected from the group consisting of fluorine, chlorine, and bromine at an elevated temperature suflicient to form and to volatilize a rhenium halide to form a volatilization product; transferring the volatilization product in agaseousstate to asitus other'than the situs of the formation of the rhenium halide; contactingthe=transferred volatilization product with water-to forma' rhenium hydrolysis product; and reducing the rhenium hydrolysis product with hydrogen to' provide the substantially free-from-potassium, purified rhenium metal powder.

8. The method of claim 7 in which the halogen is References Cited in the file of this patent UNITED STATES PATENTS 1,829,756 Noddack etal ,Nov. 3, 1931 2,594,370 Warburton Apr. 29, 1952 2,670,270 Jordan Feb. 23, 1954 FOREIGN PATENTS 575,801 Gjermany May 3, 1933 680,710 Great Britain ,Oct. 8, 1952,

OTHER REFERENCES Van Arkel: Chem. Abstracts, vol. 28; p. 5011 (1934).

Thorpes Dictionary of-Applied Chemistry, 4th ed-., vol. X, 1950, pp. 517, 518, 521-524;

Battelle Technical Review, July 1954, page77.

Hampel: Rare Metals Handbook, pages 352359, published 1954 by Reinhold Pub. Corp., N.'Y.'

Hampel: Rare Metals Handbook, pp. 360-361, published- 19.54 by Reinhold Pub. Corp., ,N.Y; 

7. A METHOD FOR OBTAINING A SUBSTANTIALLY FREE-FORMPOTASSIUM, PURIFIED RHENIUM METAL POWDER FOR METALLURGICAL CONSOLIDATION AND FABRICATION FROM A CRUDE RHENIUM METAL CONTAINING POTASSIUM, THE METHOD COMPRISING: EXPOSING THE CRUDE RHENIUM METAL CONTAINING POTASSIUM TO A HALOGEN SELECTED FROM THE GROUP CONSISTING OF FLUORINE, CHLORINE, AND BROMINE AT AN ELEVATED TEMPERATURE SUFFICIENT TO FORM AND TO VOLATILIZE A RHENIUM HALIDE TO FORM A VOLATILIZATION PRODUCT, TRANSFERRING THE VOLATILIZATION PRODUCT IN A GASEOUS STATE TO A SITUS OTHER THAN THE SITUS OF THE FORMATION OF THE RHENIUM HALIDE, CONTACTING THE TRANSFERRED VOLATILIZATION PRODUCT WITH WATER TO FORM A RHENIUM HYDROLYSIS PRODUCT, AND REDUCING THE RHENIUM HYDROLYSIS PRODUCT WITH HYDROGEN TO PROVIDE THE SUBSTANTIALLY FREE-FROM-POTASSIUM, PURIFIED RHENIUM METAL POWDER. 